ABSTRACT There is growing evidence of the role of sleep and circadian disorders in cardiovascular disease, metabolic disorders, neurodegeneration and cancer. This reflects that sleep and circadian disorders have systemic effects affecting multiple organs. While there is a growing and rapidly developing view as to the major public health significance of sleep and circadian disorders, there is a paucity of investigators in the area, particularly those employing state of the art approaches. This postdoctoral fellowship research training program is addressing this issue. The program is housed at the University of Pennsylvania (Penn). It is part of the comprehensive effort in research training by the Center for Sleep and Circadian Neurobiology at this institution. Penn was the first institution in the United States to develop in 1991 a comprehensive medical school-wide center for this activity recognizing the very multidisciplinary nature of sleep and circadian research field. Since 1991 Penn has played, and continues to play, the leading role in research training in this field. Penn has the most faculty investigators in the area of any institution nationally and the most research support. While the research training program is well established, it continues to evolve to meet changing scientific direction and needs. The program is now organized into 4 specific tracks: a) basic research; b) clinical and translational research; c) behavioral science and ?basic human research?; and d) implementation and comparative effectiveness research. The program takes advantage of the infrastructure that has been developed at Penn for research training. This includes the Office of Biomedical Postdoctoral Programs (BPP), the Masters of Science in Clinical Epidemiology, the Masters of Science in Translational Research, and the Masters of Science in Health Care Policy Research.